This invention relates to an engine control system and, more particularly, to an improved feedback control system for an engine.
As has been known, it is extremely desirable to maintain the fuel/air ratio in the cylinders at the stoichiometric or leaner than stoichiometric running condition. This will promote not only good fuel economy but effective exhaust ignition control.
Various control systems have been proposed for this purpose and a very popular system employs a feedback control employing an exhaust sensor. The exhaust sensor senses the condition of the exhaust gases and from that is able to determine whether the mixture is rich or lean in the combustion chamber from the contents of the exhaust gases. Through a feedback control system, the amount of fuel supplied and/or air supplied is varied so as to maintain the desired fuel/air ratio. This type of system is very effective.
The application of this type of control, however, to a two-cycle engine presents certain difficulties. One reason for this is that the exhaust gases in a two-cycle engine may in fact indicate a condition other than that that is representative of the combustion at the end of the combustion cycle. The reason for this is that two-cycle engines, because of their more frequent firing and their scavenging systems, can have a fresh fuel/air mixture present in the combustion chamber and also passing through the exhaust system. If this fresh mixture is mixed with the exhaust products, then the sensor will obtain a false reading.
There has, therefore, been proposed a type of system wherein the exhaust sensor actually senses the combustion products in a single cylinder immediately at the time of completion of combustion. This is done in a variety of manners and one very effective way of achieving this result is shown and described in the copending application of Masahiko Katoh, Ser. No. 08/435,715, filed May 5, 1994 and assigned to the assignee hereof. In certain embodiments of that application, the exhaust sensor receives exhaust gases from one cylinder through a port that communicates with the cylinder at approximately the time when the exhaust port opens and before the scavenge port has been opened. This gas is then transmitted to an accumulator chamber in which a sensor is positioned and this chamber is discharged to another cylinder of the engine that is operating on another cycle so that the flow will, in essence, be in a constant direction from the cylinder being sensed.
One problem attendant with exhaust sensors of this type, particularly when the sensor is an oxygen (O2) sensor is that if the engine misfires, which is usually a result of an overly rich mixture, the sensor may actually sense a lean condition. The reason is that when misfire occurs unburned fuel may deposit on the oxygen sensor and the system senses a lean mixture and thus provides additional fuel to the engine, thus aggravating the misfiring condition.
It is, therefore, a principal object of this invention to provide an improved feedback control system for an engine employing an oxygen sensor.
It is a further object of this invention to provide a feedback control system for an engine wherein a different control routine is adopted in the event of engine misfires.
It is a still further object of this invention to provide an improved misfired detection and feedback and control system for two-cycle engines.